Hi there, I have a 66 charger with a non original 383 that I just purchased last year. I checked the casting numbers and believe the block is a 68. The problem I'm having is that Im wanting to do a tune up and am getting conflicting info with regarding the spark plugs. I've always ran champions in my small blocks but this is new to me. So far I'm narrowed down to an RJ12YC and an RJ14YC. I'm pretty sure it's just the heat ranges but still unsure what to use.
Any suggestions?